This invention relates in general to data communication between computers using modems and relates more particularly to unauthorized modem access to computers. In the figures, the first digit of a reference numeral indicates the first figure in which the element designated by that numeral is presented.
In recent years widespread use of modems has occurred to enable computer users to access and transfer a wide variety of data. Modems are often used to access various databases, to transfer data between computers of different computer users and to enable remote access by a user of his or her own computer. For example, a sales representative can take a portable computer on a business trip and be able o access his or her own computer back at the office or to access a central computer to obtain up-to-date information for prospective customers. It has also become common to have a second computer at home for use outside of normal working hours or for occasions when it is convenient to work at home.
Unfortunately, such remote modem access of computers can make a computer system vulnerable to theft and/or loss of data by espionage or computer crackers. It is therefore important to prevent such unauthorized access to the extent possible. Unfortunately, many computers are now connecte together over communication networks (like that illustrated in FIG. 1) that increase the risk of unauthorized access.
FIG. 1 shows a set of users 11-17 connected to one another by a network consisting of a data switch 18 and a set of CPUs 111-113. Some of the users (11 and 12) are connected directly to the data switch, some of the users (13-15) are connected directly to a CPU, and some of the users (16 and 17) are connected indirectly to a CPU in the network. To protect the network from unauthorized external access, incoming modem access could be prohibited, but this would prevent useful or even necessary externally initiated access. Instead, modem access to the network can be centralized into one or more modem pools to centralize external access to the network. In one common approach shown in FIG. 1, all modem links to this network initiated by a user outside of this network are formed through an incoming modem pool 19 and all modem links from this network initiated by a user on the network are formed through an outgoing modem pool 110.
The modems in incoming modem pool 19 have an autoanswer capability so that when that modem is called by an outside user, the modem automatically answers the call and establishes the link to an internal user or CPU indicated by the outside user. The modems in outgoing modem pool 110 do not have an autoanswer capability so that no outside user can initiate a link to the network through outgoing modem pool 110. The effect of this is that all modem access by outside users is funnelled through the reduced set of modems in the incoming modem pool 19. Therefore, security precautions need only be applied to the reduced set of modems in pool 19.
In one type of security system called the "call back" security system, one of the CPUs (referred to herein as the "Protector") on the system ensures that only authorized users are allowed access to th network. The Protector contains a list of authorized users, the passwords of the authorized users and the phone numbers of the outside modems of these authorized users. When an outside user attempts to establish a modem link to the network, the Protector requests the outside user to enter the outside user's password. The Protector then terminates the modem access by that outside user and checks a table of authorized users to see if the entered password corresponds to the password of an authorized network user. If it does, then the Protector determines the phone number of the outside modem for that authorized user and calls that modem back. Therefore, to circumvent this protection, an unauthorized outside user must not only have determined the phone number for access to the incoming modem pool and the password of an authorized user, but must also be located at the location called by the Protector.
This call back security system limits access to only those phones listed in its list of authorized users and therefore prevents an authorized user, located away from that user's authorized phone, to access the system. This system would therefore prevent access from travelling sales representatives as well as any other systms users needing access while away from home. Therefore, some Protector systems also implement a query/response type of security system. In one example of the query/response security system, when the outside user seeks to establish modem access, the Protector queries the outside user for certain information and compares thereturned answers against listed correct answers. These questions are directed to information that should only be in the possession of the authorized user corresponding to the code entered by the user. For example, the questions might be about the user's Social Security number and his or her great anut's dog's name.
In another variant of the query/response security system, the Protector sends a coded piece of data to the outside user. This outside user then inputs this data into some type of encryption device, such as a calculator loaded with appropriate encryption code, to produce a response. Preferably, this encryption device includes a key that is unique to that user so that the received response from the user is uniquely determined. This response is then sent by the outside user to the Protector. The Protector compares the response to the correct response it should receive and allows modem access only when this response is correct.
Unfortunately, the Protector can be easily and unwittingly circumvented by any party who attaches a modem (such as modem 114) to any of the user's ports on that user's CPU on the network. Although most networks include internal protections such as the use of passwords for access to the network by internal users, it only takes one careless internal user to circumvent the internal security measures. It is therefore prudent to take all reasonable measures to prevent unauthorized access to any part of the network by unauthorized outside users because such access could compromise the data on the entire network.